This invention relates to an improved cylindrical cutter head for cutting holes in metal objects and particularly irregular metal objects. An example of the application of the cutter head is for cutting a hole in a pipe wall. It can be easily understood that when cutting a relatively large diameter hole in the wall of a relatively large diameter pipe that the tubular cutter head undergoes substantial stress during the cutting action. The reason is that when cutting initially starts the tubular cutter head engages the pipe only on portions that are 180.degree. apart. As the cutting depth increases the amount of contact of the cutter head with the pipe wall slightly increases but at no time does the full 360.degree. of the cutting head contact the pipe. Since the sidewall of a tubular cutter head is preferably relatively thin the forces encountered during cutting operations can cause the sidewall to deflect, thus, either forming an irregular shaped hole or causing more rapid wear on the teeth of the cutter head.
A cutter head having a tubular sidewall should ideally remain symmetrically circular throughout the cutting operation so that cutting action does not vary with respect to the axis of rotation of the boring bar or other member by which the cutter head is rotated.
It is normally desirable that the tubular sidewall of a cutter head be relatively thin. This is so since the tubular sidewall must be no greater in thickness than the width of the cutting teeth. Obviously, the wider the cutting teeth the more force that is required to form a hole in a pipe or other object. Ideally, the width of the teeth of a tubular boring portion of a cutter head is as narrow as possible to reduce the cutting energy required. Obviously, the tubular sidewall of the cutting head must be of thickness no greater than the teeth since the sidewall must follow the teeth through the hole as it is cut. This means that ideally a cutter head tubular sidewall needs to be as thin as possible but, at the same time, it must have sufficient rigidity to withstand the tremendous forces that are encountered in cutting through an irregular object while preserving its concentricity about its rotational axis.
Others have provided cutting heads for cutting large diameter holes in metal objects such as illustrated in U.S. Pat. Nos. 1,441,994 issued to Mueller entitled "Shell Cutter And Drill For Drilling Machines" and 1,855,873 issued to Shortell entitled "Cutting Tool". Each of these patents show a cutter head having a cutting member with a relatively thin tubular wall and a head portion that attaches to the tubular cutting member. In each case the rotatable head is of a relatively thick material that is substantially greater in thickness than that of the annular cutting member. Neither of these patents show devices where the head portion is configured to deflect or otherwise change the force applied to the annular cutting member tubular sidewall in the process of cutting a large diameter hole.
An object of the present invention is to provide an improved cutter shell having a boring portion with a tubular sidewall with teeth at the forward circumferential end and an inverted dish shaped head portion of relatively thin material. The head portion deflects in response to boring pressure. The deflection serves to apply force to the circumferential upper end of the tubular boring portion to stiffen and make it more resistant to deflection to thereby reduce the possibility of the boring portion tubular sidewall taking a non-circular shape during a boring operation.